We believe that our most recent work studying the electrical properties of neurons of the brain represents a breakthrough in understanding how potassium channels control the excitability of neuronal electrical activity, and may have a significant impact on both basic and clinical neuroscience. We have recently shown that one of the largest components of delayed outward potassium conductance in many neuronal types, during normal physiology has gone unnoticed and is the product of Na+-activated SLO2 (Slack) channels. Previous studies of potassium conductances in mammalian neurons may have overlooked this large component of outward current because the Na+ channel blocker TTX is typically used in studies of mammalian K+ channels and TTX also removes SLO2 currrents as a secondary consequence of its block of Na+ entry. Since most prior studies of the electrical properties of CNS neurons have overlooked the large SLO2 component, we propose to show its contribution to the electrical properties of neurons in several brain regions where it is prominently expressed. This will allow a more thorough understanding of the currents that determine neuronal electrical activity and may reveal SLO2 channels as useful pharmacological targets for the control of epilepsy and other seizure disorders. Because SLO2 channels are prominently expressed in the striatum they may also be a useful target in the treatment of Parkinson's Disease and in the treatment of depressive illness. In addition to showing the contribution of SLO2 channels to neuronal electrical excitability, we will also reveal more about the mechanism of SLO2 K+ current activation. We previously discovered that the SLO2 K+ current is activated by Na+ entry through a persistent inward sodium conductance. Thus, we will determine the genetic identity of one or more sodium channels that carry such a persistent sodium current capable of activating SLO2 channels. We will also investigate the functional relationships between sodium channels which carry a persistent Na+ current, and SLO2 Na+-activated channels. These experiments will be undertaken in a heterologous system where we will reconstitute a SLO2-sodium channel coupled system, and in experiments using single membrane patches from native neurons where the functional interactions of sodium channels and SLO2 channels can be studied under circumscribed conditions where sodium entry is limited to the patch.